* {
    box-sizing: border-box;
}

body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100vh;
    overflow: hidden;
    margin: 0;
    color: #444;
    background-color: #f5f5f5;
}

h1 {
    font-size: 5rem;
    color: skyblue;
    opacity: .4;
}

/* 输入框表格 */
form {
    width: 400px;
    max-width: 100%;
    box-shadow: 0 4px 8px rgba(0, 0, 0, .1);
}

form .input {
    display: block;
    padding: 1rem 2rem;
    width: 100%;
    font-size: 2rem;
    color: #444;
    border: 0;
}

form .input::placeholder {
    color: #d5d5d5;
}

form .input:focus {
    outline: none;
}

/* 待做事项 ul */
form .todos {
    margin: 0;
    padding: 0;
    background-color: #fff;
    list-style-type: none;
}

.todos li {
    padding: 1rem 2rem;
    font-size: 1.5rem;
    border-top: solid 1px #e5e5e5;
    cursor: pointer;
}

/* 已完成式样 */
.todos li.completed {
    color: #b6b6b6;
    /* 删除线 */
    text-decoration: line-through;
}

/* 提示 */
small {
    margin-top: 3rem;
    color: #b5b5b5;
}